Notifications underwent a massive overhaul in Android Lollipop, getting both a Material Design makeover and new methods that help Android sort notifications more intelligently.
In Android 5.0 and higher, you can annotate your notifications with the
setPriority() method. Low-priority notifications may be hidden from the user, while higher-priority notifications are more likely to interrupt whatever the user is currently doing.
The different priority levels are:
Notification.PRIORITY_MAX: Used for critical and urgent notifications that alert the user to a condition that's time-sensitive, or that they may need to resolve before they can continue with the current task.
Notification.PRIORITY_HIGH: Typically used for important communications ...